1. Field of the Invention
The present invention relates to a liquid jet head for forming an image, a character, or a thin film material on a recording medium by discharging liquid from a nozzle, and to a liquid jet apparatus using the liquid jet head.
2. Description of the Related Art
In recent years, there has been used an ink jet type liquid jet head for discharging ink droplets on recording paper or the like to render a character or graphics or for discharging a liquid material on a surface of an element substrate to form a pattern of a functional thin film. In such a liquid jet head, ink or a liquid material is supplied from a liquid tank via a supply tube to the liquid jet head, the ink is caused to fill minute space formed in the liquid jet head, and the capacity of the minute space is momentarily reduced according to a drive signal to discharge a liquid droplet from a nozzle which communicates to a groove.
FIG. 7 is a sectional view illustrating an ink jet head 100 of this kind which is described in Japanese Patent Application Laid-open No. 2005-306022. The ink jet head 100 includes a substrate 101 formed of a piezoelectric material, for discharging ink in an ink chamber 103 which is formed on a surface thereof, a lid member 102 placed on the surface of the substrate 101 so as to expose a part of the ink chamber 103, a manifold 105 placed on a surface of the lid member 102 and on the surface of the substrate 101, for supplying ink which flows in from an in-between tube 106 to the ink chamber 103, and a cover 108 for housing those members.
Drive power is applied from a flexible printed circuit board (FPC) 107 to an electrode (not shown) on the substrate 101 to change the capacity of the ink chamber 103 by the piezoelectric effect. Then, a liquid droplet D is jetted from a nozzle in a nozzle plate 104 to perform recording on a recording medium with the ink. By moving the ink jet head 100 or the recording medium in synchronization with the jetting of the liquid droplet, a character or graphics may be printed.
A surface of the lid member 102 is bonded to the surface of the substrate 101. The substrate 101 is formed of a piezoelectric material, for example, PZT ceramic. In order to prevent warpage of the substrate 101 due to temperature change, the lid member 102 and the substrate 101 are formed of a same material. The manifold 105 and the lid member 102 are bonded at a bonding portion A1 while the manifold 105 and the substrate 101 are bonded at a bonding portion A2. As the material of the manifold 105, from the viewpoint of weight reduction and cost reduction, a synthetic resin such as an acrylic resin, a polyimide resin, or a polycarbonate resin, or a metallic material is generally used. Therefore, bonding between different kinds of materials is carried out at the bonding portions A1 and A2. In order to prevent warpage of the substrate 101 and to prevent peeling off of the manifold 105 from the substrate 101 or the lid member 102, it is necessary to select materials of the manifold 105 and the substrate 101 so that the difference in the thermal expansion coefficient between the manifold 105 and the substrate 101 is small. Therefore, materials which may be used for the manifold 105 are limited.
Further, the bonding portions A1 and A2 are in direct contact with ink which flows through the ink chamber 103. An adhesive which is low in hardness and soft even after it hardens is generally liable to be dissolved in organic ink. Therefore, an adhesive which is required to be resistant to ink is high in hardness and adhesive strength thereof is high. On the other hand, in such an ink jet system, ink is discharged by momentarily reducing the capacity of the ink chamber 103 by the piezoelectric effect. However, ink discharge speed is affected by the characteristic frequency of the substrate 101. The ink jet head discharges ink while the ink jet head moves, and thus, change in the ink discharge speed results in displacement of the landing position of the ink.
In particular, when the hardness of the adhesive which is applied to the bonding portions A1 and A2 is high, vibrations of the substrate 101 and the lid member 102 caused by discharge of ink are propagated via the adhesive to the manifold 105 and other members for fixing the manifold 105. Then, the vibrations of the substrate 101 caused by discharge of ink is affected by other members to change the discharge speed of liquid droplets to be discharged. Therefore, there is a problem in that, depending on the drive frequency and conditions of the discharge of liquid droplets, the discharge speed varies and a liquid droplet of a target amount may not be caused to land on a target position.
Further, the surfaces of the substrate 101 and the lid member 102 to be bonded are ordinarily not flat. Therefore, thickness of an adhesive on those surfaces to be bonded varies depending on the place. Variations in the thickness of the adhesive at the bonding portions A1 and A2 affect the drive performance. Further, the adhesive used at the bonding portions A1 and A2 swells when brought into contact with ink, in particular, organic ink. When the adhesive is brought into contact with ink and swells, the thickness and the hardness of the adhesive change, and thus, there is a problem in that warpage of the substrate 101 may occur and the substrate 101 may be broken.